1. Field of the Invention
The present invention relates to a surface acoustic wave device and a boundary acoustic wave device.
2. Description of the Related Art
In recent years, a wafer-level chip-size packaging (WLCSP) technology has been developed that reduces the size of a package of a surface acoustic wave device, such as a surface acoustic wave filter, and a boundary acoustic wave device, such as a boundary acoustic wave filter, to a component chip size.
For example, as shown in FIG. 13, a surface acoustic wave device includes a piezoelectric substrate 1 and a resin substrate 7 that faces the piezoelectric substrate 1. The piezoelectric substrate 1 includes a conductor pattern having an IDT (a comb-shaped electrode) 2, a reflector 3, and a pad 4 provided thereon. The resin substrate 7 includes an external electrode 8. The piezoelectric substrate 1 and the resin substrate 7 are bonded and sealed by light curable resins 6a and 6b. The pad 4 is electrically connected to the external electrode 8 (refer to, for example, Japanese Unexamined Patent Application Publication No. 2003-37471).
When such a structure in which a piezoelectric substrate is covered and sealed by a cover is applied to surface acoustic wave devices and boundary acoustic wave devices, capacitive coupling tends to increase. In particular, when the sizes of the devices are reduced by using a wafer-level chip-size packaging (WLCSP) structure, the capacitive coupling significantly increases. An increasing capacitive coupling deteriorates the isolation characteristics and VSWR.